Aristolochic acid-associated urothelial cancer in Taiwan

Abstract

Aristolochic acid, a potent human carcinogen produced by Aristolochia plants, is associated with urothelial carcinoma of the upper urinary tract (UUC). Following metabolic activation, aristolochic acid reacts with DNA to form aristolactam (AL)-DNA adducts. These lesions concentrate in the renal cortex, where they serve as a sensitive and specific biomarker of exposure, and are found also in the urothelium, where they give rise to a unique mutational signature in the TP53 tumor-suppressor gene. Using AL-DNA adducts and TP53 mutation spectra as biomarkers, we conducted a molecular epidemiologic study of UUC in Taiwan, where the incidence of UUC is the highest reported anywhere in the world and where Aristolochia herbal remedies have been used extensively for many years. Our study involves 151 UUC patients, with 25 patients with renal cell carcinomas serving as a control group. The TP53 mutational signature in patients with UUC, dominated by otherwise rare A:T to T:A transversions, is identical to that observed in UUC associated with Balkan endemic nephropathy, an environmental disease. Prominent TP53 mutational hotspots include the adenine bases of (5')AG (acceptor) splice sites located almost exclusively on the nontranscribed strand. A:T to T:A mutations also were detected at activating positions in the FGFR3 and HRAS oncogenes. AL-DNA adducts were present in the renal cortex of 83% of patients with A:T to T:A mutations in TP53, FGFR3, or HRAS. We conclude that exposure to aristolochic acid contributes significantly to the incidence of UUC in Taiwan, a finding with significant implications for global public health.

Fig. 1.

TP53 mutational spectra in urothelial carcinomas. (A) TP53 mutations in DNA obtained from UUC in Taiwan (113 mutations). (B) TP53 mutations in DNA obtained from UUC in endemic regions of Bosnia, Croatia, and Serbia (62 mutations) (12). (C) TP53 mutations in urothelial carcinomas of the renal pelvis and ureter, worldwide (73 mutations) (16). (D) TP53 mutations in urothelial carcinomas of the renal pelvis, ureter, bladder, and nonspecified urinary organs, worldwide (696 mutations) (16).

Fig. 2.

TP53 base substitution mutations in DNA from urothelial UUCs. (A) Arrows above and below the bar representing TP53 cDNA indicate the position of mutations at A:T and G:C (purple arrows) pairs, respectively, in tumor DNA from Taiwanese subjects. Red arrows indicate A:T→T:A transversions; blue arrows show other types of mutations at A:T pairs. (B) Positions of A:T→T:A transversions on transcribed and nontranscribed strands of DNA in UUC patients from Taiwan (red arrows) and in residents of endemic regions of Bosnia, Croatia, and Serbia (black arrows) (12).

Fig. 3.

Characterization of AL-DNA adducts, using liquid chromatography electrospray ionization/multistage mass spectrometry (LC-ESI/MS/MS³), in the renal cortex of a representative Taiwanese subject with UUC. (A) The product ion spectrum of the protonated base adduct [BH₂]⁺ for the dA-AL-I adduct identified in renal cortex; (B) product ion spectrum of synthetic dA-AL-I; (C) product ion spectrum of the dA-AL-II adduct identified in renal cortex; and (D) product ion spectrum of synthetic dA-AL-II.

Fig. 4.

Incidence rates of UUC and RCC in Taiwan and the United States. (A) The age-adjusted incidence rate of UUC in Taiwan and the United States. (B) UUC/bladder cancer (BC) incidence ratio in Taiwan and the United States. (C) Age-adjusted incidence rates of UUC, BC, and RCC in Taiwanese women. (D) Age-adjusted incidence rates of UUC, BC, and RCC in Taiwanese men. All incidence results were adjusted according to the world population proposed by Segi et al. (40). Data for the United States were derived from the International Agency for Research on Cancer database (32), and for Taiwan, from the Taiwan Cancer Registry (33).